The Spanish word 'benjamín' comes from the Biblical name Benjamin, which has its roots in ancient Hebrew. The Hebrew name 'Binyamin' (בנימין) is a compound of two words: 'ben' (בן) meaning 'son' and 'yamin' (ימין) meaning 'right hand' or 'south', thus literally meaning 'son of the right hand'. This name entered Spanish through Latin 'Beniamin' and Greek 'Beniamin' (Βενιαμίν).

In Spanish, 'benjamín' has evolved to specifically mean 'youngest child' or 'youngest member of a group'. This semantic shift likely comes from Benjamin being the youngest of Jacob's twelve sons in the Biblical narrative. The word is commonly used to refer to the youngest sibling in a family or the youngest member of any group.

While 'benjamín' itself is a commonly used Spanish word, it doesn't have many etymologically related words in Spanish since it comes directly from a Hebrew personal name. However, you might encounter it in phrases like 'el benjamín de la familia' (the youngest of the family) or 'el benjamín del equipo' (the youngest member of the team).

The English name 'Benjamin' is directly related to Spanish 'benjamín', as they share the same Hebrew origin. While in English 'Benjamin' remains primarily a personal name, it's interesting to note how Spanish has adapted it into a common noun meaning 'youngest child'. The English diminutive 'Ben' is also related, being a shortened form of Benjamin.